Excavating machines for excavating tunnels can be provided with cylindrical shields which define an annular clearance with the excavated wall such that concrete or other sealing compositions can be introduced between the cylindrical shield and the wall. In this sense the shield forms a falsework or tunnel-lining form. Generally the forms are provided in sections and, after the concrete has hardened at a downstream end of the machine, the form section is removed and remounted at an upstream end of the lining which progresses in the forward direction.
The cylindrical elements can be referred to as lining elements, casings, and falsework, since generally they do not remain in place after the concrete is hardened, although one can contemplate circumstances under which the casings can remain.
In U.S. Pat. No. 4,436,448 and the corresponding German patent document No. 29 52 744, a tunnel-excavating machine utilizing the principles described and including such casing sections has been described.
As noted, the casing is formed from a number of casing sections which are disposed end to end and can be provided with centering elements for aligning each end substantially with an end of an adjoining casing element, drawbolts for securing the adjoining ends of these elements together, and sealing members which bridge the gaps between the casing elements to prevent incursion of the concrete or other aligning composition into the space surrounded by the casing elements.
The sealing elements must bridge various gap widths, depending upon the positioning of the casing elements.
While the casing elements can be composed of cast steel so as to have inwardly directed flanges or ribs at their ends and axially extending ribs bridging these flanges, in general the casing elements are composed of steel sheet or steel plate and are formed in a welded construction. In the latter case, the casing sections may be composed of segments in a casette type of structure.
The casing system with which the present invention is concerned is generally of use for the continuous placed-concrete method of lining the tunnel. In this method, as the excaving machine continues advancing through the tunnel, a casing or lining is assembled immediately behind the excavator and upstream of the previously emplaced lining sections.
The concrete is forced into the spaces between the lining sections or casing and the tunnel wall, the leading edge of the concrete being filled into a space behind a movable form member (forming part of the machine) which recedes as the concrete is pumped into the space.
In order to enable the straight casing sections to follow a curved path of the tunnel, the sections may be assembled so that the gap between them varies in width, depending upon the direction of curvature with a wedge shape. Depending upon the degree of the variation, various radii of the tunnel curves can be accommodated and depending upon the side which has the wider gap or the narrower gap, it is possible to allow the casing to follow practically any path contour which may be generated.
Depending upon the conformation of the path in space, the maximum width of the gap on one side of the casing and the corresponding minimum width at the diametrically opposite side of the casing can be determined.
In spite of the fact that gaps of various widths are required to allow the casing to assume the various curvatures necessary to follow the path of the tunnel, the gaps between the casing sections must be sealed off for a variety of reasons including the need to prevent incursion of the concrete introduced into the space around the casing. Another reason for the seals is that ground water must be excluded from the free space in the tunnel.
In addition, transverse and normal forces must be transferred by the casing sections, these forces being generated by a variety of sources. For example, they include the forces produced by the flowable concrete owing to local gravity or weight effects, local dynamic forces from the concrete pump pressure, the reaction forces by the fluid-operated cylinders which advance the excavator and the like. Centering and force-transmitting members are provided to additionally connect the casing elements. In conventional tunnel casings of the aforedescribed type, the bolts which draw the casing sections together also form the spacers or are provided with the spacers and also provide the means for taking up the forces mentioned above. They can be used to fix the width of the gap.
However, these systems are not able to withstand pressure forces so that if such axial pressure forces tending to compress the casings arise, either because of geological shift conditions or because of the way the excavator is operated, uncontrolled changes can occur in the relative positions of the individual casing elements.
To prevent this change, it is the practice to drive wood wedges into the gaps. This is a time-consuming and an expensive operation, in spite of the fact that it does not adequately secure the casing sections. Furthermore, such wedges can be removed only with considerable difficulty and thus impede the dismounting of an end section at the downstream end. Of course any wedges which are removed at this end must be reinserted when the casing section is again assembled onto the upstream end.
In the latter patent and the corresponding German patent document, there is described a hydraulic piston-and-cylinder connection between cylindrical shield sections of a tunneling machine, although not between falsework sections in place of the drawbolts or tension-screw arrangements hitherto used effectively, this arrangement links successive shield sections together.
The connecting piston-cylinder elements are generally of the double-acting type and can be operated in an active or passive mode, as desired. When they operate in an active mode, they can be individually controllable so that one shield section can be actively shifted as to its orientation and spacing with respect to the other.
When, however, a passive mode is desired, the connecting piston-cylinder arrangements can be interconnected in parallel and connected to a closed hydraulic network so that one shield section can be adjusted relative to the other in a passive manner.
Similarly one can make use of a tunnel excavator in which the shield sections are additionally connected together via an articulation or joint as in German patent document-printed application DE-AS No. 12 03 300.
In this manner manual adjustment of the individual drawbolts of the classical construction can be avoided.
While tunneling machines thus have been improved according to the principles of U.S. Pat. No. 4,436,448, as far as I am aware, they have not influenced the field of replaceable or assemblable tunnel linings or casings, possibly because the connecting piston-cylinder arrangements do not allow simple removal, replacement, mounting or adjustment of the individual casing sections.